David Cole is national legal director of the American Civil Liberties Union. Faiz Shakir is national political director of the ACLU.

The right to boycott has a long history in the United States, from the American Revolution to Martin Luther King Jr.’s Montgomery bus boycott to the campaign for divestment from businesses serving apartheid South Africa. Nowadays we celebrate those efforts. But precisely because boycotts are such a powerful form of expression, governments have long sought to interfere with them — from King George III to the police in Alabama, and now to the U.S. Congress.

The Israel Anti-Boycott Act, legislation introduced in the Senate by Benjamin L. Cardin (D-Md.) and in the House by Peter J. Roskam (R-Ill.), would make it a crime to support or even furnish information about a boycott directed at Israel or its businesses called by the United Nations, the European Union or any other “international governmental organization.” Violations would be punishable by civil and criminal penalties of up to $1 million and 20 years in prison. The American Civil Liberties Union, where we both work, takes no position for or against campaigns to boycott Israel or any other foreign country. But since our organization’s founding in 1920, the ACLU has defended the right to collective action. This bill threatens that right.

The Israel Anti-Boycott Act is designed to stifle efforts to protest Israel’s settlement policies by boycotting businesses in Israel and the occupied Palestinian territories. The bill’s particular target is the boycott, divestment and sanctions (BDS) movement, a global campaign that seeks to apply economic and political pressure on Israel to comply with international law.

Whether one approves or disapproves of the BDS movement itself, people should have a right to make up their own minds about it. Americans engage in boycotts every day when they decide not to buy from companies whose practices they oppose. Students have boycotted companies that sold clothing manufactured in sweatshops abroad. Environmentalists have boycotted Nestlé for its deforestation practices. By using their power in the marketplace, consumers can act collectively to express their political points of view. There is nothing illegal about such collective action; indeed, it is constitutionally protected.

In NAACP v. Claiborne Hardware Co., the Supreme Court in 1982 upheld the right of NAACP activists to hold a mass economic boycott of segregated businesses in Mississippi. The court stated that the boycotters’ exercise of their rights to “speech, assembly, and petition . . . to change a social order that had consistently treated them as second-class citizens” rested “on the highest rung of the hierarchy of First Amendment values.”

This is not to say that all boycotters are automatically free speech heroes; indeed, BDS advocates have themselves at times shut down Israeli academics or speakers to the detriment of academic freedom. Thus, it’s understandable that free speech advocates might not immediately identify BDS supporters as victims of censorship. But when government takes sides on a particular boycott and criminalizes those who engage in a boycott, it crosses a constitutional line.

Cardin and other supporters argue that the Israel Anti-Boycott Act targets only commercial activity. In fact, the bill threatens severe penalties against any business or individual who does not purchase goods from Israeli companies operating in the occupied Palestinian territories and who makes it clear — say by posting on Twitter or Facebook — that their reason for doing so is to support a U.N.- or E.U.-called boycott. That kind of penalty does not target commercial trade; it targets free speech and political beliefs. Indeed, the bill would prohibit even the act of giving information to a U.N. body about boycott activity directed at Israel.

The bill’s chilling effect would be dramatic — and that is no doubt its very purpose. But individuals, not the government, should have the right to decide whether to support boycotts against practices they oppose. Neither individuals nor businesses should have to fear million-dollar penalties, years in prison and felony convictions for expressing their opinions through collective action. As an organization, we take no sides on the Israeli-Palestinian conflict. But regardless of the politics, we have and always will take a strong stand when government threatens our freedoms of speech and association. The First Amendment demands no less.